<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>元素的层级</title>
    <style>
        body{
            font-size: 60px;
        }
        .box1{
            width: 200px;
            height: 200px;
            background-color: #bfa;
            position: absolute;
            /* 
                对应开启了定位的元素，可以通过z-index属性来指定元素的层级
                z-index是一个整数作为参数，值越大，层级越高 元素就优先显示
                如果元素的层级一样，则有限显示靠下的元素
                祖先元素不会盖住后代元素
             */
             /* z-index: 3; */

        }
        .box2{
            width: 200px;
            height: 200px;
            background-color: rgba(255, 0, 0,0.5);
            position: absolute;
            top: 50px;
            left: 50px;
            /* z-index: 2; */
        }
        .box3{
            width: 200px;
            height: 200px;
            background-color:yellow;
            position: absolute;
            top: 100px;
            left: 100px;
            /* z-index: 1; */
        }
        .box4{
            width: 100px;
            height: 100px;
            background-color: orange;
            position: absolute;
        }
    </style>
</head>
<body>
    <div class="box1">1</div>
    <div class="box2">2</div>
    <div class="box3">3
        <div class="box4">4</div>
    </div>


</body>
</html>